From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeffrey A Law <law@cygnus.com>
To: Craig Burley <burley@gnu.org>
Cc: davem@dm.cobaltmicro.com, d.love@dl.ac.uk, egcs@cygnus.com
Subject: Re: ix86 double alignment (was Re: egcs-1.1 release schedule) 
Date: Tue, 23 Jun 1998 03:32:00 -0000
Message-id: <17700.898578696@hurl.cygnus.com>
References: <199806221829.OAA07477@melange.gnu.org>
X-SW-Source: 1998-06/msg00782.html

  In message < 199806221829.OAA07477@melange.gnu.org >you write:
  > Well, I'm willing to not try to do any special aligning for
  > EQUIVALENCE and COMMON for now.  If we can just get 64-bit
  > alignment for stack-allocated VAR_DECLs -- which generally
  > won't include EQUIVALENCE (and certainly not COMMON) -- we'll
  > have made a *huge* improvement in g77 performance, especially
  > its *repeatability* of performance measurements.
Yup.  But considering the release schedule, I'd be happy if we could
just get the stack aligned properly without breaking the ABI, then
iterate to getting automatic variables aligned relative to the stack.

If we can get more done before the release, then great, but I wouldn't
want to hold things up on this issue if we can avoid it.

  > (Without this improvement, egcs 1.1 will often appear *substantially*
  > worse than the combination of g77 0.5.22 and gcc 2.7.2.3 on lots of
  > widely used Fortran code, assuming users are using -malign-double.)
Well, we still have -malign-double as an option for the x86 port, so
if they use it they presumably would see comparable performance, right?

Actually, I'd expect generally better performance because we do  handle 
alignments for static store items in a reasonable manner, which is a
significant improvement by itself).

  > Note that I suggested the gcc architecture (machine descriptions,
  > etc.) be modified to include a more fine-grained expression of
  > alignment requirements.  E.g. distinguishing hardware requirements
  > (even instruction requirements, such as `ld' vs. `ldd' on SPARCv8)
  > from ABI requirements from ideal performance settings.  But this
  > suggestion was turned down at the time -- some seven years ago!
Sigh.  Yea, it really seems like something we should have -- then
again, there's been little gcc emphasis on the x86 in the past and
it's the most likely benefactor of such stuff.

jeff